<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>
<body>
    切换秒数<input type="number" name="len" id="time" value="15"/>
    <p></p>
    <button id = "run">开始</button>
    <button id = "stop">结束</button>
    <script type="text/javascript" src="popup.js"></script>
</body>
</html>